在 mysql 查询中使用 group by 获取学校计数和年级计数

Question

我想获得总学校的计数，其中包括该学校的总成绩，如果学校计数不应该考虑重复的学校 ID。和包括学校 1 和学校 2 在内的总成绩的计数，我想要使用单个查询来实现，是否有可能得到预期输出中提到的结果。

表：

school_id      grade

  1             1

  2             1


  1             3

  1             4

预期输出：

1) school count=2

2) grade count for individual school like

    school_id   grade_count

      1           3
      2           1

3)  total grade count  (school 1+school2)=4

我使用了这个 Mysql 查询，但它没有按要求工作以获取所有三个输出

Mysql查询：

select count(*) as total_school,count(grade) from (SELECT grade FROM schools group by school_id)X 

Answer 1

SELECT 
  `school_id`,
  (SELECT COUNT(DISTINCT `school_id`) FROM `school_grade`) as different_school_count,
  COUNT(*) as school_count,
  COUNT(DISTINCT `grade`) as grade_count,
  (SELECT COUNT(*) FROM `school_grade`) as total_grade_count
FROM
  `school_grade`
GROUP BY `school_id`

输出：

| school_id | different_school_count | school_count | grade_count | total_grade_count |
|-----------|------------------------|--------------|-------------|-------------------|
|         1 |                      2 |            3 |           3 |                 4 |
|         2 |                      2 |            1 |           1 |                 4 |

http://sqlfiddle.com/#!9/9132c7/16